One of the things he pointed out is that while the food economy and the energy economy have until now always been independent, they are now utterly linked due to the growth of biofuels. We've had food crises before--but they have been much more event related. We could see the end of them.

Things have changed.

It is not an inexpensive proposition to turn agricultural products into energy. If the price of oil is under about $70 a barrel, it just isn't a profitable switch. But when energy prices are high (and right now oil is just about at its record high of $115 a barrel), the price of grains go up because there is increased demand.

In our industrial food system, high grain prices mean high prices for dairy products and beef as well. (Under a traditional system, cows eat only grass and are pastured on land that is not particularly usable for other agriculture.)

Chickens, accustomed to foraging on a mix of foods including lots of garden bugs, are now fed "vegetarian" feed which is predominantly grain. We even feed the fish we eat grain these days. So the price of chicken and fish also rises.

And even agricultural products that are totally unconnected to ethanol production wind up going up in price as farmers sacrifice planting other crops in order to grow more food for fuel.

The corollary is that non-food crops grown for fuel can force food crops off of good agricultural land.So, as the price of fuel goes up, the price of food goes up.

The price of oil seems unlikely to drop substantially. But let's imagine what would happen if it did: grain prices would suddenly plummet because of the oversupply as oil companies turned away from biofuels. Many starving people would be able to afford to eat immediately, but almost as quickly, local farmers would loose their livelihoods.

Disturbingly, this is exactly the pattern that can occur when wealthy countries dump subsidized grain as food aid on poor countries. Grain from abroad floods local markets, removing the ability for many farmers to support themselves. They move to cities in an effort to find some sort of work. When they lose their farms, they then cannot feed the local community and the people of their country.

We drive, they starve. The mass diversion of the North American grain harvest into ethanol plants for fuel is reaching its political and moral limits.

"The reality is that people are dying already," said Jacques Diouf, of the UN's Food and Agriculture Organization (FAO). "Naturally people won't be sitting dying of starvation, they will react," he said.

The UN says it takes 232kg of corn to fill a 50-litre car tank with ethanol. That is enough to feed a child for a year. Last week, the UN predicted "massacres" unless the biofuel policy is halted.

We are all part of this drama whether we fill up with petrol or ethanol. The substitution effect across global markets makes the two morally identical.